Watercraft that are propelled by water jets are popular. One particular type, the personal watercraft, such as a Jet Ski® made by Kawasaki of Kobe, Japan, is used in racing and for amusement. The water-jet propelled watercraft (hereinafter “watercraft”) operates between two extremes of performance. First, there is a need for speed during straight sections of a race course. Second, there is a need for power in turns, or “holes” that form when the watercraft partially or completely submerges during a sharp turn. For speed, a narrower output nozzle is preferred, which increases the speed of the output jet and also the watercraft. For power, a wider nozzle is needed to increase the flow mass and so improve the momentum exchange with the watercraft. Various approaches have been used to deal with these divergent requirements.
One approach is to simply choose either a narrow or a wide nozzle. Some nozzles are adapted to receive various interchangeable inserts that create various constant-diameter nozzles, depending on the race course. Racers on courses with long straight stretches would use a narrower nozzle, while racers on courses with many turns would prefer to equip with wider nozzle.
Various approaches to mechanically squeezing a flexible annular member have been developed. U.S. Pat. No. 5,256,090 to Woolley uses a mechanical linkage to compress to flexible partial cylinders together to vary the nozzle diameter. U.S. Pat. No. 4,092,010 to Carlson. Jr., uses a mechanical wringing action about a flexible nozzle tube to change nozzle diameter. Mechanical manipulation of leaves, as used in modern fighter jet engines, has also been applied to watercraft. One difficulty with such devices is the propensity of debris in the water to become lodged or entangled in the mechanical working or leaves.
U.S. Pat. No. 3,279,704 to Englehart, et al., discloses a VARIABLE NOZZLE (see FIG. 18) for a water jet-propelled watercraft with an annular flexible member adhered to the tapered tail pipe member for adjusting an annular flow of water out of the tailpipe. The annular flexible member is expanded using fluid pressure. Englehart's annular flexible member, in an unexpanded state, narrows the flow through the nozzle. Englehart teaches the use of the annular flexible member with a control element, which appears to be an axially moveable pintle valve. Englehart's annular flexible member is illustrated as being attached by adhesion, in an unreliable way, in that the force that expands the annular flexible member tends to remove the annular member at one end, and the other end wraps around a sharp structural edge, tending to cut the annular member as it flexes. Because Englehart's annular member is on a tapered tail pipe member, the force of the exit water impinges on the annular member at a higher pressure than water merely passing beside anon-tapered tail pipe wall. Englehart discloses a control system for this water jet nozzle that uses boat speed and water jet speed out the exit nozzle as the inputs, and controls the water jet speed to approximate the boat speed. This control strategy maximizes propulsive efficiency miles per gallon) but not racing performance.
U.S. Pat. No. 3,214,903 to Cochran discloses a JET BOAT NOZZLE (see FIG. 19) comprising an annular flexible inflatable tube of triangular cross-section to provide convergent flow in a watercraft nozzle. Cochran's tube is inflated with air or hydraulic fluid. Cochran's tube creates a tapered nozzle, even in its minimally inflated state, and so the force of the exit water impinges on the tube at a higher pressure than water merely passing beside a non-tapered tail pipe wall. Additionally, the nozzle diameter is always reduced by Cochran's triangular tube. Cochran's tube is bonded to a receptacle that is attached within the tail pipe of a watercraft. Given the variable nature of the forces acting on it, bonding does not appear to be highly reliable. Neither Englehart's nor Cochran's inventions are found in the modern marketplace. Cochran uses the same control strategy as Englehart.
Therefore, a need exists for an improved variable-dimension water jet. In particular, a need exists for a better way to attach a flexible annular member within a water jet nozzle. A need also exists for improved variable-dimension water jet nozzle that does not reduce the diameter of the exit nozzle in a minimally inflated state. A need also exists for an improved variable-dimension water jet nozzle that does not subject the flexible annular member to water pressure forces unnecessarily. A need also exists for an improved variable-dimension water jet nozzle that operates at a lower pressure than previous art. A need also exists for an improved variable-dimension water jet nozzle that can be fitted to watercraft exit nozzles designed for interchangeable inserts. A need also exists for an improved variable-dimension water jet nozzle responsive to a control system that is based on engine rpm and vehicle speed. A need also exists for an improved variable-dimension water jet nozzle and its control system mounted on a watercraft.